Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $125.91   13.637%   $143.0803   $143.08   $143.10   $143.10  
  Purchase #2 $41.84   11.350%   $46.5888   $46.59   $46.60   $46.60  
  Purchase #3 $157.51   12.668%   $177.4634   $177.46   $177.45   $177.50  
  Purchase #4 $201.37   7.511%   $216.4949   $216.49   $216.50   $216.50  
  Purchase #5 $222.43   8.569%   $241.49   $241.49   $241.50   $241.50  
  Purchase #6 $110.57   13.708%   $125.7269   $125.73   $125.75   $125.70  
  Purchase #7 $105.29   13.809%   $119.8295   $119.83   $119.85   $119.80  
  7 purchase totals = $964.92       $1,070.6738   $1,070.67   $1,070.75   $1,070.70